Trouble shooting a plasma cutter

Esab 550. I had cut three holes in 1/4" plate when it just stopped cutting in
mid-stream. No spark. I checked the consumables, they're all new.
I still get air when I hit the trigger. The overheat light isn't on. It still
doesn't work the next day.
I checked continuity of the power cable with an ohm meter and it has continuity,
almost zero resistance. Is there some other way to test it? Could it have
continuity at rest but fail under load?
The trigger wires obviously have continuity because the trigger still works the
solenoid valve to supply air to the torch.
It just won't cut anything.
The book suggests replacing the HF unit. How can I test the HF unit and what
kind of money are we talking about to replace it?
--
Jack
Reply to
Jack Hunt
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This gets rather involved. How electronics savy are you ? I'd call ESAB, get a quote, and/or a repair quote from yer local welding depot. This is the fear of all of these electronic inverter-based machines, since they are complex, expensive to repair. Is it under warranty?
Reply to
Mr Wizzard
Hm, do you have a schematic? Can you open the case? Some things should be easy to troubleshoot, such as whether you have open circuit voltage. High frequency unit probably has two terminals that connect to the welding cable. If you attach a wire to one of them and carefully let it close to another, you would see sparks.
Donot test terminals where high voltage is present, with a regular multimeter, it will blow it. I would suggest to use a throwaway $3.99 harbor freight multimeter.
There are some lethal voltages present inside plasma cutters, so, be careful and conservative, but you can find out a lot by testing various points with a multimeter. I am sure that many people here are experts on plasma cutters (I am not one), and could help you if you are able to take pictures, post them on a webpage and tell them what you have done.
i
Reply to
Ignoramus31174
Look for loose wires. It's kind of common on those machines. Is yours a Esab USA or Italian model. Esab changed to USA built on those machines.
Jack Hunt wrote:
Reply to
svande48
I once built a digital frequency counter from a sack of parts and a pre-cut PC board. 30 years later it still works.
That's the second resort. I fear the invoice would read:
Arm Leg Firstborn child Pint of blood
Probably not. I've had it over a year.
-- Jack
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Reply to
Jack Hunt
Well kwel, so you know about P-N/N-P transisstor junctions, and gate drive circuits etc then, good. So, yeah, there were a coupla posts in this thread that were good advice. i.e. check for the availability of a schematic. Failing that, check some obvious things. Opern er up, find that big mean ole power supply (cap bank), and carefully check for voltage there. Do the "smell test", look for burnt traces, blown fuses, chared resistors, etc. Failing that, find the switching element(s), the gating components (diode blocks, snubber diodes), and any/all of the power electronic components. Get the numbers off of them (to see what they are), isolate them, and start checking them. (IGBT's, SCR's, diodes, etc). You have a scope? (one with at least 1,000 volt max input). If not the insulated input Tektronix battery operated scope, make sure to use an isolation transformer if its an A/C. But check to see if the main high voltage supply is working. There's a chance that you can fix it, expecially if you know how to test a diode junction with a multimeter, and have a rough idea of how switchers work.
Reply to
Mr Wizzard
Jack -
I don't have that one ... - Have you 'cycled' the consumables ? - likely there is a switch behind the source - Maybe a simple fix. Is the source fouled ? - metal melted into it ?
Test - look - try...
Martin
Martin Eastburn @ home at Lions' Lair with our computer lionslair at consolidated dot net NRA LOH & Endowment Member NRA Second Amendment Task Force Charter Founder IHMSA and NRA Metallic Silhouette maker & member
Jack Hunt wrote:
Reply to
Martin H. Eastburn
Before you do anything check that the electrode ,cap /diffuser and nozzle are tight. There is a safety interlock that prevents pilot arc initiation if they are missing or loose.
Pete
Reply to
Pete
If everything 'just stopped working' as you say, then its almost certainly a safety interlock. If the torch front end parts are fitted properly, and you've got power, my guess is your air pressure is too low. Most air pressure safety cutouts operate at 3.8 bar (~45psi). you should be sure you have around 60psi available WHEN RUNNING.
Reply to
Potblak
I hope you're right. I haven't had time to check anything yet. I may get chance to work on it today, it's raining and I can't do anything else.
That's one of the first things I checked. There's a gauge right on the side of the box and it shows good pressure, although I will agree that it may be the air pressure limit switch that has malfunctioned.
It's connected to a 140psi source and is regulated inside the machine cabinet to 60 psi.
I was in the middle of putting 4 holes in the bucket of my front end loader so I could attach some shop-built forks making it into a fork lift. I had cut the holes in one of the forks. I laid the fork in place in the bucket and transferred marks for the holes in the bucket. I started cutting the first hole in the bucket, punching through and making a half circle when it just stopped. I still get air to the torch when I push the trigger but no spark.
**This may or may not be significant** I cut the holes in the forks with the forks sitting on a couple of sawhorses. The power cable was draped across the top of one of the horses, and the fork fell over, firmly pinching the power cable where it crossed the sawhorse. The very next cut I made was the one where it just stopped in mid cut. I used an ohm meter to check continuity between the torch and the other end of the cable and got continuity. Is there another check I can make without electrocuting myself or blowing up a good digital tester that only goes to 600v?
I bored the holes in the other fork with a drill press. Then I drug the drill press outside, carefully set the bucket on the drill press table, and drilled the holes with the drill press.
The forks are made from 2x4 steel tubing with 1/4" walls. I did all the cuts with the plasma cutter last year when I made them, and welded them with a Lincoln 225AC welder and 7018 electrodes. Yesterday while cleaning up my scrap steel pile, I ran one of the forks under a tree stump. It lifted the whole back end of the tractor off the ground. Who says you can't weld anything solidly with a buzzbox?
-- Jack
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Reply to
Jack Hunt
Sorry, Jack, I missed your quick reply as I was off to bed here in Melbourne Australia. I can't find an "Esab 550" plasma cutter in my info. Can you be more specific on the model? I assume its quite new. as one of the other guys mentioned, there is a safety interlock which cchecks the front end parts are fitted correctly. The signal from this (a closed circuit for most torches) is passed back to the machine by two fine wires along the cable group which will consist of; :the main Power cable (probably with air along it. May look a bit like a TIG torch cable) :the HF (pilot arc) cable (May look like an auto ignition cable) :two trigger wires :two safety interlock wires. The safety and trigger wires may have a common ground, so there would be only three wires total.
DON't do any testing with the machine even plugged into the power!
Now you can open the machine front panel and see where each set of wires connects. The multimeter should show you easily which are the trigger and which are the safety interlock wires. I suspect the interlock wires are open circuit. Good luck, Martinatbinzeldotcomdotau
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Reply to
Potblak

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